1. Field of the Invention
The present invention relates to terminal connection verifying methods for verifying connections between terminals of circuit blocks in semiconductor circuit devices and CAD (computer-aided design) apparatuses for implementing the terminal connection verifying methods. In particular, the present invention relates to a terminal connection verifying method for verifying connections between terminals of an analog circuit macro and terminals of a logic circuit, both circuits being included in a semiconductor circuit device, and a CAD apparatus for implementing the terminal connection verifying method.
2. Description of the Related Art
Recently, in many cases, semiconductor circuit devices include not only logic circuits but also analog signal processing circuits, that is, analog macros. The analog macros each handle an analog signal which conveys information by using the potential level of the signal, and which differs from a logic signal that conveys information on the basis of an “H (high)” or “L (low)” state of the potential level of the logic signal.
This makes it impossible for a logical simulator to accurately handle the analog signal. Thus, it is not easy for the logical simulator to accurately verify connections between terminals of an analog macro and terminals of a logic circuit. This is because the logical simulator handles, as a signal whose logic is indefinite, an analog signal whose potential level is in a state other than the H or L state.
Here, to accurately verify connections between circuit terminals, it is possible to use an analog simulator capable of handling both a logical signal and an analog signal. However, it takes a long time to perform verification of connections between circuit terminals by using the analog simulator, and the verification is expensive.
In addition, to reduce the verification time and cost, it is possible that the connections between the circuit terminals be verified by visual inspection of a designer. However, in the verification by the visual inspection of the designer, there is a possibility that human error may occur.
Accordingly, to reduce the verification time and cost, a method that uses a logical simulator to verify connections between terminals of an analog macro and terminals of a logic circuit has been proposed. By way of example, the following method (see, for example, Japanese Unexamined Patent Application Publication No. 2004-273476) has been proposed.
At first, a semiconductor integrated circuit is assumed in which a digital circuit block, a bias circuit that outputs bias signals in response to a signal from the digital circuit block, and analog circuit blocks that operate in response to the bias signals are connected to one another. In this case, since the bias signals are analog signals, the logical simulator handles the bias signals as signals whose states are indefinite. Thus, the logical simulator cannot verify connections of wires that transmit the bias signals between the digital circuit block and the analog circuit block. Accordingly, in the bias circuit, a first pseudo pulse generating circuit is provided. The first pseudo pulse generating circuit generates a first pseudo pulse signal in the “H” or “L” state which has a different pulse width. In addition, in each analog circuit block, a second pseudo pulse generating circuit is provided. In response to the first pseudo pulse signal, the second pseudo pulse generating circuit generates a second pseudo pulse signal in the “H” or “L” state. When the pulse width of the first pseudo pulse signal and the pulse width of the second pseudo pulse signal are equal to each other, it is determined that connection is established between a predetermined terminal of the analog circuit block and a predetermined terminal of the digital circuit block.
The verifying method, disclosed in Japanese Unexamined Patent Application Publication No. 2004-273476, for verifying the connections between the terminals of the analog macro and the terminals of the logic circuit, has a problem in that, to verify the connections, an additional number of clocks for the longest pseudo pulse width is required. The word “longest” is used because, when analog signals exist in a circuit to be verified, to differentiate the analog signals, pseudo pulses having different lengths are assigned to the analog signals.
The verifying method also has a problem in that, since a pseudo circuit whose operation differs from the actual circuit operation is needed, in addition to verification of the actual circuit operation, a period in which the pseudo circuit operates is additionally needed.
In addition, the verifying method, disclosed in Japanese Unexamined Patent Application Publication No. 2004-273476, for verifying the connections between the circuits, is effective in verifying connections between the logic circuit and the bias circuit and in verifying connections between the bias circuit and the analog circuits. However, the verifying method has a problem in that it is not effective in verifying connections between a logic circuit and an analog circuit such as an analog-to-digital conversion circuit or a digital-to-analog conversion circuit.
This is based on the following reason. Each bias signal can be replaced by a logical signal having a fixed pulse width since the bias signal has a substantially fixed potential. However, a logical signal input from the digital circuit, or a logical signal output to the digital circuit changes the potential of an analog signal handled by the analog-to-digital conversion circuit or the digital-to-analog conversion circuit. Thus, in each pseudo pulse generating circuit, disclosed in Japanese Unexamined Patent Application Publication No. 2004-273476, for generating a single pulse, the change in potential cannot be represented.